The treatment of the surface of an article with more or less abrasive solid particles has been known for a long time, either for descaling or for improving the state of the surface, for example for obtaining a matt or shiny appearance.
When the article to be treated is metallic, then a method known as the "drum" method is usually employed, according to which the article is placed free in a mass of particles contained in a receptacle and this receptacle is driven, for example in rotation around a horizontal or inclined axis passing through it, so as to stir the article and the particles together.
This method cannot be used when the article to be treated is markedly lower in density than the mass of particles, because it then tends to adopt a position above this mass.
It is known, in this case, to immobilize the article in relation to the receptacle so that the solid particles may successively touch it as the receptable rotates. FR-A-1,057,952 describes a device comprising receptacles with a vertical axis, into which the articles carried by a vertical sliding rod which is placed above them are lowered. JP-A-5,882,669 describes a piece of apparatus of the same kind, but in which the vessel has an axis which is inclined at 30.degree. to 45.degree. to the vertical, its upper end being open and provided with a collar to retain the particles and in which the article is maintained by virtue of a vertical sliding rod, in the lowest part of the volume of the receptacle.
Devices of this kind cannot be adapted for the treatment of fragile articles such as pieces of furniture or parts of pieces of furniture, because problems arise when the article enters the mass of the solid particles; unless this is done very slowly, a considerable force is needed to push the article in, even when the receptacle is rotating, and the article runs the risk of being damaged.
The method generally employed consists in pouring the particles out of the receptacle while the article is introduced and then reintroducing these partices gradually into the receptacle, preferably while the latter rotates. These operations are slow and costly.
To give an idea of this, it may be stated that, to treat a chair or armchair frame, a mass of glass beads of the order of 1500 kg is generally employed.
In Application DE-A-2,520,399, it has been proposed to use a receptacle capable of switching from a vertical position, in which the article is above the mass of particles, to a horizontal position, in which the article is partially immersed in the mass. This system is bulky, and the tilting operation needs to be slow in order not to damage the article.
In Patent Application EP-A-0,084,483 it has been proposed to simplify the emptying and refilling operations of the receptacle by virtue of an auxiliary receptacle, concentric with the principal receptacle and integrally fastened thereto; the auxiliary receptacle communicates with the principal receptacle and makes it possible to place the particles aside when the article to be treated is placed in position and when it is removed. The device has the disadvantage of being bulky.